New Insights into Auxin Biosynthesis
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چکیده
It is well known that auxins, primarily indole-3-acetic acid (IAA), exert control over many important developmental processes in plants, including cell division and cell expansion, vascular tissue differentiation, root initiation, apical dominance, gravitropic and phototropic responses, flowering, fruit ripening, leaf senescence, and abscission of leaves and fruit. Despite the wealth of knowledge regarding the physiological roles and importance of auxin in controlling plant development, the biosynthetic pathway to IAA remains enigmatic, perhaps due to the existence of multiple pathways and, possibly, functional redundancies among various participating enzymes (Bartel, 1997; reviewed in Normanly and Bartel, 2000). Further complicating the issue, most of the IAA in plants is conjugated (a portion reversibly) to a variety of amino acids, peptides, and sugars. The starting point for IAA synthesis is in the Trp biosynthetic pathway, and in recent years it has become generally accepted that there exists a “Trp-independent” pathway (branching off from the Trp biosynthetic pathway at a Trp precursor, such as indole) as well as a Trp-dependent pathway. The notion of a Trp-independent pathway is based, in part, on the observation that mutants of Arabidopsis with reduced levels of Trp synthase have increased amounts of IAA conjugates (Normanly et al., 1997). However, Müller and Weiler (2000a) have now cast doubt on the existence of a Trp-independent pathway to IAA in Arabidopsis. Using isotope labeling, they showed that the apparent increase in IAA conjugates in Trp synthase mutants in fact results from degradation of indole-3-glycerophosphate, the IAA (and Trp) precursor that hyperaccumulates in the mutants, suggesting that the Trp-independent pathway to IAA may be an artifact (Müller and Weiler, 2000a). Also, New Insights into Auxin Biosynthesis
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تاریخ انتشار 2001